Harding, a Conservative peer, will be replaced by TalkTalk's current managing director, Tristia Harrison, while Carphone Warehouse cofounder Sir Charles Dunstone will become TalkTalk's executive chairman.

TalkTalk's shares on the London Stock Exchange jumped 8% off the back of the announcements.

"After seven extraordinary and fulfilling years, during which we have transformed TalkTalk's customer experience and laid the foundations for long term growth, I've decided it's time for me to start handing over the reins at TalkTalk and focus more on my activities in public service," Harding said in a statement.

Harding's exit was announced as TalkTalk revealed its latest set of results, which show that the company's revenues had fallen to £435 million, from £459 million for the same time last year.

TalkTalk said the fall in revenue was expected and only a "short term" issue.

Dunstone said that Harding had been a "tireless, energetic and effective force for good from the day she joined TalkTalk," adding that she "has helped transform TalkTalk into a much stronger business."

He added: "I'm excited at the prospect of spending more time on TalkTalk, beginning with delivering another successful performance this year."

Dunstone will be replaced by Lord Ian Livingston. He is a Scottish businessman, a Conservative peer, and the former CEO of BT. He is also deputy chairman of the Dixons Carphone business that Dunstone is leaving.